[tex-k] TeXbook: typo in answer to exercise 20.7

[Igor Liferenko]

Hi all,

In TeXbook, answer to exercise 20.7, it is written that TeX says:

    #1<-x

But TeX actually says:

    !1<-x

Regards,
Igor

P.S.

Can anybody explain what means the following extract in the answer?

    which is different from {